Checking if taxes are enabled when verifying if ECE should be displayed

[wjrosa]

Fixes STRIPE-538

Changes proposed in this Pull Request:

This is a minor fix for an edge case when a store enabled taxes but disabled them afterwards. The value of woocommerce_tax_based_on would still exist, making the express checkout buttons hidden when falling into the tax-based logic for virtual products.

Testing instructions

• Check out and build the develop branch on your test environment
• Connect your Stripe account
• Enable taxes for the store
• Set the taxes to be based on the customer's billing address
• Enable the express payment methods (Google Pay, Apple Pay, Link)
• Now, disable taxes
• As a shopper, add a virtual product to your cart (make sure the product is set to "taxable")
• The express checkout buttons are not displayed
• Checkout and build this branch instead (fix/check-if-taxes-are-enabled-when-checking-for-ece-display)
• Confirm the buttons are now displayed

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• Covered with tests (or have a good reason not to test in description ☝️)
• Tested on mobile (or does not apply)

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Post merge

• Added testing instructions to the Release Testing Instructions wiki page (or does not apply)
• Added the needs docs label (or does not apply)
• Included this PR in the Release Thread scope (or does not apply)

[annemirasol]

I believe we fixed this before in #3563, and somehow lost it during refactors. Thanks for catching and fixing.

Added a suggestion to use the WooCommerce-provided function.

[github-actions]

📈 PHP Unit Code Coverage Report

Package	Line Rate	Health
includes/payment-methods/class-wc-stripe-express-checkout-helper.php	22%	❌
Summary	44% (7164 / 16356)	❌

[annemirasol]

I think we should set $taxes_enabled to true in the unit tests, except for the two cases that specifically test for the "taxes are disabled" scenario. That way, we know the behavior is due to the scenario it is testing, and not only because taxes are enabled/or disabled, e.g. ECE should always be available in the Pay for Order page.

[annemirasol]

LGTM, thanks for fixing!

Just realized I was the one who removed the check when I added per-product tax logic 🙈